This invention relates to signature gathering machines. Signatures, which are folded sheets, are stored in a plurality of pockets. The signatures are gathered by pocket feeders which place them one on top of another on a delivery chain or conveyor. The collected signatures are known as a book. In the type of binding known as saddle binding, the signatures are gathered on a saddle, with the two legs of the signature astride the saddle. After all the signatures are collected, the book is advanced stepwise along the saddle to a stitching station where the book is stitched along the backbone, usually by staples. Stepwise movement of the book to the stitching station is accomplished by grippers on a gripper bar as will be explained in more detail below. The gripper bar is reciprocated along a horizontal path.
After the book is stitched it is advanced to a delivery station where there is a pair of rollers for delivering the completed book to yet another station, usually a trimming station where the head and foot of the book are trimmed. The book is lifted upward off the saddle and introduced into the bight of the delivery rollers by a so-called tucker blade.
Signature gathering machines of the type described have been subject to vibration problems in the delivery chain or conveyor. Vibration of the delivery chain tends to joggle the signatures as they are carried along on the conveyor. This causes the margins of the signatures to become uneven with the result that the books cannot be cleanly trimmed.